Wall Street is also concerned. Shares of LinkedIn are off more than 1 percent on a day when tech stocks overall are rallying.

A link to the reported list led to a text file called combo_not.text, hosted on a Russian server. That file contains 6,458,021 40-character hexadecimal strings, which is consistent with the report of almost 6.5 million hashed passwords allegedly leaked.

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The initial story was triggered after a user in a Russian forum claimed that he hacked and uploaded almost 6.5 million LinkedIn passwords onto the Web.

Many of the hashed passwords reportedly include the word "linkedin," which The Verge and other sources believe lends credibility to the claim.

LinkedIn passwords are encrypted using the SHA-1 algorithm, which is considered highly secure. But some reports say that groups of hackers are working on decrypting the passwords. Complex passwords won't be easy to crack, but simple ones are vulnerable.